Created attachment 690428[details]
virtual network definition
Description of problem:
Actual support for IPv4 would be nice but as a started, virt-manager should at least tolerate valid ipv6 specifications in the virtual network's xml file.
Attached is an example definition and a screenshot of what happens
Version-Release number of selected component (if applicable):
Fedora 18, virt-manager-0.9.4-4

(copying my virt@fedora posting here for completeness)
No plans at this point. Right now there isn't anyone explicitly working on new
virt-manager features, besides people popping up to scratch an itch.
When I've had time I've been working on the gtk3 port and virtinst merge, but
even once that's done the first big feature I'll likely work on is snapshot
support.
I'd love to get IPv6 support in virt-manager, so if anyone is interested in
giving it a shot I'm happy to mentor.

My knowledge about python can be written on the head of a pin but I am going to give it a shot. While virt-manager may have some shortcomings, I have looked into gnome-boxes and find it does not meet my needs whereas virt-manager does.
Right now I am doing most of my network creation, maintenance, and operation using virsh net-* but it would be handy if virt-manager connections could at least start and stop a network which includes IPv6.
I don't intend on carrying on any discussion here. Would you rather have my questions on the virt-tools-list or direct to you?

Yes please let's continue on virt-tools-list.
I know you've filed other patches too, but if virt-manager fails to even start/stop an ipv6 network that should be an easy fix. If you bring it up on list I can probably patch it quickly, just provide an example network XML and the virt-manager --debug output when reproducing.
The harder parts will be exposing the ipv6 details in the UI, and adding ipv6 support to the 'new network wizard'.
Also, if you are going to poke at the virt-manager code, use the gtk3.2 branch which will become upstream master fairly soon. It's also quite easy to use
git clone git://git.fedorahosted.org/virt-manager.git
cd virt-manager
git checkout gtk3.2
./virt-manager

This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle.
Changing version to '19'.
(As we did not run this process for some time, it could affect also pre-Fedora 19 development
cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.)
More information and reason for this action is here:
https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora19